Welding machine



Aug. 1961 D. STOLZ ET AL 2,996,603

WELDING MACHINE Filed Jan. 2, 1959 5 Sheets-Sheet 1 iju n iu 12a g '784. I02 A I 4 5 1 um I 20% I 1 6b 3/ g; loo 1% Zg I W ll7o 7i 5 70 B I IIH 5 E? 5 5 at I H 1111 UL.

INVENTORS Dasmcmo S'rouz. Y CHARLES E..LETscm-:

ATTORNEY Aug. 15, 1961 D. STOLZ ET AL 2,996,603

WELDING MACHINE Filed Jan. 2, 1959 5 Sheets-Sheet 3 will INVENTORSDasmcmo STOLZ.

CHARLES E..LETSCHE ATTORNEY Aug. 15, 1961 Filed Jan. 2, 1959 E 98 I S 5Sheets-Sheet 4 N N S 5 98 we 8 I w um R:

\ E. =l I i F16. IO INVENTORS Desmouo STOL'Z.

CHARLES E. Luscue BY ATTORNEY United States Patent O 2,996,603 s WELDINGMACHINE Desmond Stolz and Charles Letsche,Milwaukee, Wis.,

assignors to Acro Welder Mfg. 00., lVIilwaukee,-Wis., a

corporation of Wisconsin Filed Jan. 2, 1959, Ser. No. 784,504 28 Claims.(Cl.'219 89) This invention relates to a magnetic force welding machineand particularly to provision of structural refinements permitting ofgreater precision in the various welding operations which such machinesare capable of performing.

In the early forms of magnetic welding machines the movable electrodewas carried on a spindle fixed to an air ram which permitted moving theelectrode to and from the work. During the welding operation themagnetic force acting on the armature exerted the extra force on thespindle which gave rise to the superior welding operation for which suchmachines have become noted. During the welding operation the spindledesirably moves a small distance as the metal melts. This movement isquite small but must take place in a very short period of timeparticularly since the advent of electronic timing mechanisms which havemade it possible to effect the weld in a fraction of a cycle (of 60cycle current). The inertia of the spindle or electrode becomes a veryreal factor when the short welding time is considered. Even though themotion is very small it was found the inertia attendant upon having theelectrode carried by the air ram was suificient to prevent obtainingoptimum results. In an effort to reduce the inertia of the spindle, theconstruction shown in Wakely application Serial Number 633,784, nowPatent Number 2,905,804, issued September 22, 1959, was evolved. In thisconstruction there was a lost motion connection between the piston ofthe air ram and the spindle which permitted the spindle to move freelyor be disengaged from the air ram during the welding operation. Thisresulted in a marked improvement in the quality of the weld.

The electronic timers utilized with magnetic welding machines aregenerally designed to initiate the flow of current at a predeterminedpoint on the current waveform. The air ram has been employed toestablish the initial pressure on the work and this pressure wasgenerally of an increasing nature and if the desired pressure wasreached at a point unsatisfactory for initiating the welding cycle, thetimer would automatically delay the weld until the right part of thecurrent waveform was reached. In the meantime, the pressure could riseWell above the desired pressure on the electrode. Hence, the priorconstructions have not achieved a fully satisfactory control over thepressure applied to the electrode. It has been suggested to overcomethis failing of the prior constructions by utilizing a spring loadingmechanism which comes into play upon attaining a predetermined loadingon the electrode. The objection to such a system is that it introducesmechanical elements having poor inertia and follow-up characteristicsand under certain conditions the springs could actually rebound in anundesirable way so as to exert a negative rather than a positive force.

The primary object of the present invention is to improve upon thefollow-up and pressure applications of the prior art.

In carrying out the above objects, a structure has been evolved whichlends itself to application of safety features to these magnetic weldingmachines to positively preolude injury to the operator should hisfinger, for example, be caught between the moving electrode and the workas the electrode moves toward the work. The structure also lends itselfto positive control of the firing "ice of the welding operation in thatthe welding operation cannot be initiated until the correct pressure hasbeen applied to the electrode.

In the magnetic welding machine there has evolved a so-called delayedforge technique which utilizes a holding magnet which supports thearmature in opposition to the force magnet which must overcome theholding magnet to attract the armature and deliver it forcibly against astop on the spindle so as' to transmit a forging blow to the spindle ata desired point in the welding operation. The relationship of the forceof the holding magnet to the force of the force magnet plus the time ofinitiating the flow of current through the force magnet determine thetime lag in delivering the forging blow. It is obvious that the armaturemust be pulled off the holding magnet at a precise moment in order toaccomplish the desired function. When it is again realized that thiswelding operation deals in fractions of cycles of 60 cycles current, itwill be appreciated that timing of this pull-off becomes highlyimportant. In the prior constructions the holding magnet Was so mountedas to introduce a variant in the time of pull-01f.

Another object of this invention is to provide a holding magnetconstruction which reduces the likelihood of variable pull-offcharacteristics as explained above.

Other objects and advantages will be pointed out in, or be apparent fromthe specification and claims, as will obvious modifications of the twoembodiments shown in the drawings, in which:

FIGURE 1 is a front view of the top portion of the present magneticwelding machine with a portion of the housing broken away to show thearrangement of switches;

FIGURE 2 is a front view, partly in section, of the portion lyingimmediately below the structure illustrated in FIGURE 1;

FIGURE 3 is a vertical section taken on line 3-3 in FIGURE 1 toillustrate the details of construction of the hydraulic ram and loadingmechanism;

FIGURE 4 is a section taken on line 4-4 in FIG- URE 1;

FIGURE 5 is a section taken on line 55 in FIG- URE 1;

FIGURE 6 is a horizontal section taken on line 6--6 in FIGURE 2 andillustrates the more compact holding coil or magnet arrangement of thepresent invention;

FIGURE 7 is a schematic representation to illustrate the generalposition of the parts and switches at the moment the electrode contactsan obstruction such as the finger between the electrode and the work;

FIGURE 8 is a schematic showing similar to FIGURE 7 but illustrates themanner in which the automatic reversal of the spindle motion isaccomplished;

FIGURE 9 shows the normal operation of the mechanism when no obstructionis encountered and at the moment before the electrode contacts the work;

FIGURE 10 shows the manner in which the switches are actuated toinitiate the welding operation;

FIGURE 11 shows a modified form of the air cylinder wherein only onesource of pressure is utilized as opposed to the double source used inthe primary form of the invention; and

FIGURE 12 is a generally schematic representation of the presentstructure coupled with a wiring diagram to aid in understanding of thepresent structure.

In order to simplify the present disclosure as much as possible theframework of the machine is not shown except to the extent necessary toillustrate the parts wherein the invention lies. Similarly the lower orfixed table portion of the machine in which the fixed electrode issupported is not shown. This fixed electrode does ap- 3 pear inschematic form in FIGURES 2 and 7 through 10 as well as the schematicFIGURE 12.

The movable electrode 10 (see FIGURE 2) is carried in fitting 12 at thelower end of spindle 14. Power is supplied to the electrode through theflexible braided bus 16 as is customary in this art. Spindle 14 isguided for vertical movement in the linear bearings 18 and 20. Thesebearings provide a minimum of frictional resistance to linear motion ofthe spindle 14 and a maximum of lateral support. Since the bearings arewell spaced vertically the spindle 14 is accurately guided and has goodresistance to column action. The framework 22 is provided with verticalposts 24, 24 which support the single turn coil 26 which surrounds thecore 28 which is magnetized when current is passed through the coil 26to thereby exert an attractive magnetic force on armature 30. It shouldbe noted that the drawing illustrates the coil 26 connected through busbar 32 to the flexible bus bar 16 so that the coil will be energizedwhen current is passed to the electrode. This is the customary practicealthough the coil and the electrode can be in separate circuits to beseparately energized if it should be desirable to alter the timing inthis respect.

Armature 30 is slidably mounted on the upwardly projecting sleeveportion 34 of adjustable stop nut 36 which is held in place on thespindle by lock nut 38. The armature is restrained against rotary motionby the fixed guides 40, 40 secured to the side plates 42, 42 of theframe. The upwardly projecting sleeve portion 34 provides a good bearingsurface for the armature (which is provided with an internal bushing)and the stop nut 36 determines the lowermost position of the armaturewith respect to the spindle. Thus, the stop nut 36 is utilized todetermine the spacing between the armature and the force magnet 28. Thisconstruction is generally similar to that shown in the aforesaid Wakeleyapplication. It will be noted that FIGURE 2 illustrates the movingelectrode 10 in a raised position while the dotted line illustrates thelower position of the electrode when it is contacting the work. In thisposition, the armature will be similarly lowered and will be quite closeto the force magnet 28.

The aforesaid Wakeley application shows an upper magnet which isutilized in the delayed forge welding technique and which was subject tocertain drawbacks. The present structure shows an improved version ofthe holding magnet. The improved magnet is shown as the annular coil 44positioned inside the concentric magnetic sleeves 46, 48 and retainedtherein by the non-magnetic annular nut 50. This assembly is fixed onthe magnetic plate 52 having apertured projecting ears 54 through whichthe screws 56 depend to permit vertical adjustment of the holding magnetstructure by means of adjusting nuts 58, 58 which are retained inposition by lock nuts 60, 60.

As now well understood in this art, this holding magnet is utilized tohold the armature 30 in an elevated position at the start of the Weldingoperation. The magnetic force exerted by the force magnet 28 builds upin accordance with the timed sequence and the effect on armature 30 is,of course, determined by the spacing between the armature and the forcemagnet. When the force exerted by the force magnet on the armatureovercomes the force of the holding magnet, the armature 30 is pulledaway from the holding magnet and rapidly accelerated until it strikesthe stop nut 36 to deliver the forging below to the spindle. It will beappreciated that in this delayed forge welding operation the pull-offcharacteristic of the armature from the holding magnet must be quiteaccurate with respect to time. The previous constructions have employedholding magnets which were dimensionally similar (in plan view) to thearmature. This led to difiicnlties in that any variations in the pulloifof the armature could result in canting the armature 'on the sleeve 34and introduce a variable factor which is undesirable for obviousreasons. By bringing the present holding coil into a concentricarrangement as illustrated in FIGURES 2 and 6, the pull-offcharacteristics have been vastly improved and the accuracy of the timeof delivery of the delayed forge blow has been improved as a directresult. It will be appreciated that the armature has a close sliding fiton sleeve 34 as distinct from the rather great clearance shown in thedrawings for illustrative purposes. It should be emphasized that theconcentric holding coil, which lies within the projected dimensions ofthe hub portion of the armature, is considered a marked advance over theprior art and is one of the points of novelty in the presentconstruction.

Thus far mention has been made of vertical movement of the spindle andelectrode without describing how the vertical movement is accomplished.The structure employed in effecting this movement is shown in FIGURES 1and 3 which, it will be understood, illustrate the structure extendingabove that shown in FIGURE 2. As may be seen in these figures, thespindle 14 projects up through the upper linear bearing 20 and the topcross-plate 62 of the frame for connection through the inner shaft 64 ofthe concentric shafts 64, 66 by means of pin 68, the ends of whichproject into the slots 70 in the bottom of the outer concentric shaft 66to prevent rotation of the shafts relative to each other. The outerconcentric shaft 66 is secured to piston 72 in the air cylinder 74. Itwill be noted there is one air line connection or conduit 76 at the topof the cylinder and another conduit 78 at the bottom of the cylinder andit will be appreciated that introduction of air pressure above thepiston 72 will force the piston down and expel air from below thepiston. Reversing the direction of the air flow will, of course, reversedirection of the piston.

In the preferred form of this invention, the piston actually constitutesa separate cylinder arrangement with a separate air supply introduced atfitting 8t) and through the tubing 82 which is slidable through thegaskets to prevent leakage. This air supply is introduced into chamber84 above diaphragm 86 as seen clearly in FIG- URE 3. The diaphragm isprovided with a rigid diaphragm pad 88 which is movable between thelimits defined by contact of the pad 88 with the shoulder 90 in thebottom of chamber 84 and contact of the pad (with the flexible diaphragmsandwiched between) with the upper shoulder 92. The pressure in chamber84 holds the diaphragm pad against the lower shoulder during downwardmotion of the piston as shown in FIGURE 3.

The diaphragm pad is connected to a central boss 94 which is biasedupwardly by a rather light spring 96 compressed between the boss and thebot-tom of the well in the inner shaft 64 into which the boss 94projects. This acts to bias the diaphragm pad and the inner shaft apartto the extent determined by contact of the inner shaft flange 98 withthe upper extremity of the outer shaft 66 at the point at which it isfixed in piston 72. It will be noted there is slight clearance betweenthe inner shaft flange 98 and the underside of pad 88 and thisclearance, as will appear more fully hereinafter, is quite important. Itwill be appreciated that if the piston is moving downwardly and thedownward motion of spindle 14 is prevented, either by contact with workor an obstruction, the inner shaft would tend to move upwardly withrespect to the outer shaft. During the relative motion permitted byreason of the slight clearance mentioned above, the only force exertedon the spindle will be that of the light spring 96. Of course, when theinner shaft flange 98 contacts the bottom of diaphragm pad 88 the fullforce of the actuating pressures will again be felt at the elect-rode.

Collar 100 fixed on the lower portion of the outer shaft 66 has alaterally projecting bracket 102 on which adjustable switch actuators104, 106 are mounted. These switch actuators are biased downwardly bytheir respective compressed spring 108, 110 so as to be yieldableupassaeos wardly when the force of the biasing springs has beenovercome. These switch actuators are adapted to cooperate with andactuate switches C and B carried on the bracket 112 secured on spindle14 by cap screws 114 and having a rearwardly projecting portion providedwith a suitable vertical groove cooperating with the guide 116 carriedby frame bracket 118 to prevent rotary motion of the switch supportbracket 112. This bracket also supports a vertical arm 120 upon whichswitch A is supported with its actuating pin projecting downwardly forcooperation with actuating plunger 122 which is adjustably supported onarm 124 with a similar biasing spring 126. The arm 124 is carried byvertically slidable member 128 retained in the spring loaded guidebracket 130. The spring load on this bracket will hold member 128 in itsadjusted position and will permit sliding motion of the member in amanner to be described hereinafter.

FIGURE 12 gives a schematic representation of the circuit and controlsfor the machine described above. Since the holding coil 44 is quiteseparate electrically from the rest of the structure, it is well topoint out that the holding coil which attracts the armature is providedwith a suitable D.C. current supply which can be varied in magnitude byrheostat 132 and the flow can be regulated by switch 134. The AC. powersupply is brought in through lines 136, 138 which lead to timer 140, thedetails of which are not important here. These timers are customarilyelectronic timers capable of very precise control over current flow.Line 136 is connected to wire 142 which leads to switches A and B whichare connected in parallel across line 142 and line 144. Switch A isnormally open while switch B is normally closed and, hence, as long asone of these switches is closed wire 144 will be provided with current.This wire leads to the coil 146 of a relay. The other lead of coil 146is connected to line 148. The other AC. power supply line 138 isconnected to line 150 as well as leading to the timer. Line 150 includesone terminal of the start-reset switch 152 as well as including oneterminal of holding switch 154. The reset switch 152 is biased open andis of the momentary-closed type. When this is closed momentarily therelay 146 will be energized by a circuit from line 136 through line 142and either switch A or B to line 144, through the coil 146 and to line148, the reset switch 152, and line 150 back to the other power line138. When the coil is energized, the armature will close the holdingswitch 154 which is in parallel across the coil with the reset switch.Therefore, upon release of the reset switch 152, the holding switch 154will continue the energization of the relay. Switch 156 is also operatedby the relay and closure of this switch will act to supply current tothe coils 158, 168 of the solenoids 162, 164 which respectively operatevalves 166, 168 which regulate the supply of air to the air cylinder 74to actuate piston 72. Valves 166, 168 are shown in the positions theyoccupy when solenoids 162, 164 are not energized. Under these conditionsair is supplied to cylinder 74 below piston 72 while the top portion ofthe cylinder is connected to atmosphere through valve 168. This, ofcourse, will result in raising the piston 72 in cylinder 74.

Solenoids 162, 164 are connected in parallel. As pointed out above,closure of the holding switch 154 and of switch 156 will provide currentfrom line 150 through the holding switch 154 to line 170, through switch156 to line 172 which leads to both coil 158 and coil 160. These coilsare, in turn, connected to line 174 which leads to foot switch 176which, when closed, connects to the power line 136. Therefore, when thefoot switch is closed the solenoids 162, 164 are energized to actuatevalves 166, 168 and reverse the flow of air to cylinder 74 and thus movethe piston 72 downwardly.

After the start-reset switch has been momentarily closed to establish acircuit through the holding switch .154 an to c ose switch 156, theopera ion of the piston is regulated by the foot switch. Reference tothe wiring diagram will demonstrate that if at any time both switches Aand B are open, the circuit through relay coil 146 Will be broken andswitches 154, 156 will open. Switches A and B are employed to introducea safety feature in the present machine. The safety feature will beexplained below and has not been found in prior art structures.

Before considering the details of the safety arrangement the descriptionof the wiring diagram should be completed. It will be noted that switchC is connected to the timer 140. This switch will be closed if allconditions are safe and when the machine is ready to be fired. At thispoint the timer will take over and determine at what point on thecurrent waveform the machine will actually be fired. As will appear morefully hereinafter, the proper pressure will be maintained on theelectrode during any waiting period required between the closure ofswitch C and the actual firing under the control of timer 140. Thispressure will be maintained without introducing any mechanical lag, aswill be pointed out later.

The wiring diagram also shows leads from the timer to the transformer178, the secondary of which is connected to bus bar 180 which takes oneturn around the core 28 and then leads through the flexible lead 16 toelectrode 10 and the circuit is made through the work pieces 182, 184 tothe lower electrode 186 which is connected to the secondary through asuitable bus bar 188.

To place the present machine in operation the startreset button isdepressed momentarily to establish the holding circuit and closeswitches 154, 156. The sliding member 128 which supponts the actuator122 for switch A is then raised to its uppermost position. After thishas been done, the foot switch 176 is closed to energize the solenoidvalve and lower the piston 72 until the electrode 10 contacts the work.As the piston moves down bracket 112 carrying switch A will also movedown in contact with the actuator 122 for switch A. This will tripswitch A and will continue down and will then move the member 128carrying the actuator 122 down to the limit determined by contact of theelectrode with the work. At this point, the actuator has been properlypositioned since the switch A will thereafter be closed any time theelectrode contacts the work. Actually the closure of switch A will takeplace slightly before contact is made but this will be a very shortdistance precluding the possibility of any obstruction between the workand the electrode, such as the operators finger. Now then, actuator 106carried by the outer shaft 66 in position above switch B is so adjustedthat it will actuate (open) switch B if there is relative motion betweenshaft 64 and shaft 66. As pointed out above, there can be relativemotion between these two shafts to the extent of the clearance betweenthe shaft flange 98 and the bottom of diaphragm pad 88 during which timethe only force which would be felt at the electrode would be the forceof the light biasing spring 96. Switch B and its actuator are adjustedso as to trip within this distance and, hence, if the operators fingershould be caught between the downcoming electrode and the work (asillustrated in FIGURE 7) this relative motion will take place and switchB will be tripped to its open position as shown in FIGURE 8. Now then,since the spindle has not moved down far enough for switch A to beclosed, the circuit through the holding coil of the relay will be brokenand, hence, switches 154 and 156 will open. This will immediately eifectreversal of valves 166 and 168 (as shown in FIGURE 8) to raise thepiston and prevent injury to the operator. During the time in which therelative motion takes place to actuate switch B, the only force whichthe operator would feel on his finger is the force of the light biasingspring 96. It will be obvious that with the holding coil having beendeenergized, it will be necessary to press the reset button in order toreestablish the operation of the ,mflt hine.

2,99e,eos

If the operators finger had not been in the way, the piston wouldcontinue its downward movement and switch A would be actuated as shownin FIGURE 9. Since switch A is in parallel with switch B the holdingcoil circuit will be maintained even though switch B will subsequentlybe opened when the electrode contacts the work as shown in FIGURE andprevents further downward movement of the inner shaft while the outershaft and the piston continue moving downwardly. Reference to FIGURE 1will demonstrate that the actuators for switches B and C are so spacedthat switch B will open prior to closure of switch C. This is necessaryfor the safety reasons pointed out above as well as being necessary toinsure that the piston will move downwardly with respect to the innershaft before the circuit through switch C can be closed. Thus, the partswill assume the positions shown diagrammatically in FIGURE 10 by thetime switch C closes. At this time, it will be noted, the diaphragm iscompletely free of connection with the piston except through theflexible diaphragm. Therefore, the pressure in chamber 84 is the onlypressure acting on the electrode and this pressure can be accuratelyregulated to achieve a precise degree of loading on the electrode so asto establish the desired pressure before switch C is closed. Thispressure can be maintained accurately even though the piston continuesmovement downward (as it does) and, therefore, the pressure on theelectrode will remain constant during any waiting period after closureof switch C for the timer to reach the desired point on the AC. currentwaveform for the firing. This, therefore, achieves an accurate controlover the pressure.

When the switch C is closed to fire the welder through the timer and thecurrent flows between the electrodes, there will be some slight meltingof the work pieces 182, 184 and at this time the follow-up action of theelectrode becomes important. The present arrangement achieves betterfollow-up than the structure shown in the Wakeley application mentionedabove in which there was a lost motion connection between the piston andthe spindle. Reference to FIGURE 10 will show that the gap between theinner shaft flange and the underside of the diaphragm pad has been takenup so that there is virtually a solid connection between the diaphragmpad and the spindle at the moment of firing. Now then, chamber 84 andits associated diaphragm are selected to provide a large volume withrespect to the motion necessary and since this is at an elevatedpressure, the follow-up action will be quite fast. The spindle has thearmature acting directly on the spindle at the moment the follow-up isneeded and the spindle is aided by the pressure on the upper side ofdiaphragm 88. Therefore, the present spindle cuts free of the piston andis aided by the loading pressure. The superior follow-up action achievedby this construction results in superior welds.

After the welding current has passed through the electrode, which, itwill be remembered, takes but a very short period of time, the pistonwill have continued travelling down with respect to the diaphragm andthe diaphragm will finally contact the upper flange inside chamber 84whereupon the connection between the piston and the diaphragm and theinner shaft and, hence, the spindle and electrode become solid again andthe pressure applied through conduit 76 above the piston acts on thespindle and, hence, an increased pressure can be achieved at the end ofthe weld operation. This type of increased pressure operation isparticularly desirable in certain types of projection welding.

From the above discussion it will be apparent that the initial movementof the piston and spindle is achieved with the pressure provided abovethe piston and after contact is made with the work the loading pressureis that pressure in chamber 84. which can be completely independent ofthe pressure above the piston. After the piston has moved relative tothe diaphragm to the extent permitted by the vertical space between thediaphragm and the bottom side of the inner flange 92 in chamber 84, theinitial pressure (that is, the pressure above the piston) can beutilized again for electrode loading purposes. In this connection, itwill be of interest now to refer to FIGURE 11 which shows a variation ofthe structure just described in that only one pressure source isutilized. This pressure is applied to conduit 200 and acts both on thetop side of the piston and in the chamber 202 above diaphragm 204. Inthis arrangement it will be appreciated that the loading pressure inchamber 2% cannot be different than the pressure applied through conduit200 since they have a common source. However, the present arrangementstill achieves those desirable features of precise control of theloading pressure at the initiation of the welding operation and thefreedom of the spindle from the piston during the followup action whichis still aided by pressure above the diaphragm. The structure shown inFIGURE 11 is not as desirable for complete versatility as that describedwith respect to the principal embodiment of the present invention.However, for certain types of limited application the structure ofFIGURE 11 will prove satisfactory.

In view of the above description, it will be apparent that the presentwelding machine achieves improvements over prior art structures inseveral respects. One of these points is the new construction of theholding magnet concentric with the spindle and lying within theprojected plan area of the hub of the armature so as to insure against,or at least minimize, any canting eifect of the armature when pullingoff the holding magnet. This, in turn, results in more precise controlof the moment of impact in the delayed forge welding technique.

Another marked advance in the present structure is achieved by reason ofwhat might be termed a double cylinder arrangement wherein one cylinderis used to actuate the piston which accounts for the major travel of thespindle while a second cylinder is utilized for loading and follow-uppurposes. As a result of the double cyinder arrangement shown in thedrawings, it is now possible to provide the welding machine with veryaccurate and reliable safety features through the use of switches A andB in the manner noted above. In the normal course of operation, it willbe remembered, switch A will close prior to opening switch B and, hence,the circuit through the relay will be maintained and switches 154 and156 will be maintained closed so as to insure the correct operation. If,however, switch B is opened prior to closure of switch A, as can happenonly when there is an obstruction between the electrode and the work,then the relay coil 146 will be de-energized to open switches 154, 156which, in turn, will reverse valves 166, 168 and cause the piston torise to its uppermost position and permit removal of the obstruction. Itwill be remembered that during the period in which switch B is caused tooperate, the only force which can be applied to the obstruction is thatforce of the light biasing spring 6.

If, on the other hand, there is no obstruction in the path and thecircuit through the relay coil 146 is maintained, switch C will beclosed at the point in spindle travel in which the proper pressure mustbe applied to the spindle since the diaphragm pad is moved off its lowerrest. Also it will be remembered, this insures that there is room leftfor travel of the diaphragm downwardly with respect to the piston toinsure rapid follow-up. This rapid follow-up takes place completelyindependentty of the inertia of the piston and, hence, can be veryrapid, particularly when it is remembered that the followup action isaided by the loading pressure, which pressure is applied to a relativelylow mass mechanism.

It will be appreciated that certain features of this invention areapplicable to non-magnetic welding machines. Similarly, the inventionhere permits of variations within the spirit of the invention. For thesereasons the invention is to be limited only by the scope of the claims.

We claim:

1. In a welding machine having a fixed electrode, a moving electrode, afluid ram operatively connected to the moving electrode for moving theelectrode, a second fluid ram including a loading chamber interposedbetween the first ram and the electrode and operative upon the movingelectrode contacting the work to load the electrode independently of thefirst ram, the loading chamber of the second ram being pressurized toestablish a constant load on the electrode and having a volume greatenough to limit to a small value the pressure changes incident tomovement of the second ram during the welding operation.

2. A welding machine according to claim 1 including means operative inresponse to interruption of electrode movement towards the work prior tocontact with the work to reverse movement of the first ram.

3. A welding machine according to claim 2 in which the last named meansincluding lost motion means operative upon contact of the movingelectrode with an object to effect transfer of the force applied to themoving electrode from the first to the second ram, means biasing thelost motion means so the only force applied on the electrode during thetransfer is the biasing force, and switch means operative during thetransfer to reverse movement of the first ram in response to relativemovement between the rams.

4. A welding machine according to claim 3 in which there is a secondswitch operative just prior to contact of the electrode with the work toshunt the first switch to thereby prevent reverse movement of the firstram upon contact with the work.

5. A welding machine according to claim 1 in which the first ramcontinues movement toward the work after the electrode contacts thework, and means responsive to a predetermined movement of the first ramafter electrode contact with the work to close the welding circuit.

6. A welding machine according to claim 1 in which each ram includes acylinder and a piston, the cylinder of the second ram being located inthe piston of the first ram.

7. A welding machine according to claim 6 in which the piston of thesecond ram is connected to the electrode through a lost motionconnection, spring means biasing the lost motion connection to itsmaximum lost motion position whereby the lost motion must be taken upagainst the force of the spring on contact of the electrode with thework, the piston of the second ram being connected solidly to theelectrode after the lost motion is taken up whereupon the fluid pressurein the second ram can act to load the electrode.

8. A welding machine according to claim 7 including electric circuitmeans operative to control fluid flow to the first ram, switch means insaid circuit means to reverse fluid flow to the first ram during takingup the lost motion, and switch means operative to shunt the first switchmeans when the electrode reaches a predetermined distance from the work.

9. A welding machine including an electrode, first and second fluid ramsserially connected to the electrode both of said rams including apressure chamber, fluid pressure means connected to the pressurechambers for actuating both rams, the first ram being operative to movethe electrode towards the work, the second ram being operative uponcontact of the electrode with the work to exert a loading force on theelectrode, the first ram being disengaged from the electrode when thesecond ram is effective and the pressure chamber of the second ram beingpressurized to establish a substantially constant load on the electrodeand having a volume great enough to limit to a small value the pressurechanges incident to movement of the second ram during the weldingoperation.

10. A welding machine according to claim 9 in which the first ramcontinues movement relative to the second ram while the second ram iseffective, and means operative upon the first ram travelling apredetermined distance with respect to the second ram to render thefirst ram operative to act on the electrode again.

11. A Welding machine according to claim. 9 in which the rams haveseparate fluid pressure supplies.

12. A welding machine according to claim 9 including means for closing awelding current circuit when the second ram is effective.

13. A welding machine according to claim 10 including spring meansinterposed between the first and second rams to be effective in theperiod of time between contact of the electrode with an object and thesecond ram becoming eflective whereby the only force acting on theelectrode during that period is the spring force.

14. A welding machine according to claim 13 including switch meansoperative during said period to reverse flow to the fluid rams toreverse the direction of electrode travel.

15. A welding machine according to claim 14 including a switch forshunting the switch means just prior to contact of the electrode withthe work.

16. In a welding machine having a fixed electrode, a moving electrode, afluid ram operatively connected to the moving electrode for moving theelectrode, a second fluid ram interposed between the first ram and theelectrode, each of said rams including a cylinder and a piston, thecylinder of the second ram being located in the piston of the first ram,so that the second ram loads the electrode independently of the firstram when the electrode contacts the work, means for establishing acontrolled pressure above the second piston to maintain a substantiallyconstant load on the electrode and the cylinder of the second ram havinga volume great enough to limit to a small value the pressure changesincident to movement of the second ram during the welding operation.

17. A welding machine according to claim 16 wherein said last namedmeans comprises a number of fixed openings leading from the pressurespace above the first piston to the space in the cylinder above thesecond piston.

18. A welding machine according to claim 16 including a secondarychamber in communication with the space in the cylinder above the secondpiston so that the variation in volume due to movement of the secondpiston in the cylinder produces little change in pressure in thecylinder.

19. A welding machine including a stationary electrode and a moveableelectrode, a first ram operatively connected to the moveable elect-rode,a second ram positioned within the first ram and connected to themoveable electrode, both of said rams including a loading chamber, fluidpressure means connected to the loading chambers for actuating bothrams, the first ram being operative to move the electrode towards thework, the second ram being operative upon contact of the electrode withthe Work to exert a loading force on the electrode, the first ram movingrelative to the second ram when the second ram is operative, a switchsecured to the second ram, a switch actuator secured to the first ramand positioned to engage the switch, whereby said switch is actuated byrelative motion between the rams and means responsive to actuation ofthe switch to reverse the motion of the first ram when the second ramengages an obstruction.

20. A welding machine according to claim 19 including a second switchresponsive to a predetermined movement of the second ram relative to thelocation of the stationary electrode to shunt the first switch.

21. In a welding machine having a fixed electrode, a moving electrode, afirst ram operatively connected to the moving electrode, a second fluidram interposed between the first ram and the electrode to load theelectrode independent y of the first mm, the second rem haw ing achamber of large volume and having piston means actuated by the pressurein the chamber, limit means within the chamber for limiting motion ofthe piston means in the direction reducing the size of the chamber.

22. A welding machine including an electrode means for moving theelectrode to and from the Work, a fluid ram interposed between themoving means and the electrode, the ram having a chamber adapted to beconnected to a pressure source to establish a desired loading force bythe pressure in the chamber, the ram being independently operative toload the electrode after the moving means has moved the electrode intocontact with the work with sutficient force to equal the loading forceexerted by the ram, the chamber of the ram establishing a generallyconstant load and having a volume great enough to limit to a small valuethe pressure changes incident to movement of the electrode during thewelding operation.

23. A Welding machine according to claim 22 in which the moving means isa ram the pressure in which builds up on contact of the electrode withthe work until the pressure equals the loading pressure in the firstnamed ram at which time the first named ram becomes effective to loadthe electrode.

24. A welding machine according to claim 23 including fluid pressuremeans operative to load the electrode during and after the weldingoperation, the pressure means being operative to damp motion of theelectrode incident to the welding operation.

25. In a welding machine having a fixed electrode, a moving electrode, afiuid ram operatively connected to the moving electrode for moving theelectrode, a second fluid ram interposed between the first ram and theelectrode and operative upon the moving electrode contacting the work toload the electrode independently of the first ram and means fordelivering a sudden supplementary ferce to the electrode during thewelding operation, the second ram being operative to damp rebound motionof the electrode occasioned by said sudden force.

26. In a welding machine having a fixed electrode, a moving electrode,piston means for moving the moving electrode into an operative positionwith respect to the fixed electrode, and diaphragm means for loading theelectrodes independently of the piston means, said piston meansincluding an internal pressure chamber, the diaphragm means beingresponsive to the pressure in the chamber.

27. In a welding machine having a fixed electrode, a moving electrode, afluid ram for moving the moving electrode into operative engagement withthe fixed electrode and including a pressure chamber within the ram, adiaphragm responsive to the pressure in the chamber, and meansresponsive to the movement of the diaphragm to independently load theelectrode after it has been moved into engagement with the fixedelectrode.

28. In a welding machine having a fixed electrode, a moving electrode,piston means for moving the moving electrode into an operative positionwith respect to the fixed electrode, said piston means including aninternal pressure chamber, diaphragm means responsive to the pressure inthe pressure chamber for loading the electrodes independently of thepiston means, said pressure chamber having a large volume sufficient tolimit to a small valve the pressure changes incident to movement of thediaphragm means during a welding operation and means for limiting therelative movement of the diaphragm with respect to the piston.

References Cited in the file of this patent UNITED STATES PATENTS1,327,792 Thornton Ian. 13, 1920 1,976,552 Friesen Oct. 9, 19342,312,938 Stieglitz Mar. 2, 1943 2,358,826 Purat Sept. 26, 19442,494,847 Welch Jan. 17, 1950 2,650,977 Welch Sept. 1, 1953 2,776,362Welch Jan. 1, 1957 2,862,100 Jones Nov. 25, 1958 2,883,516 Bek Apr. 21,1959 2,892,068 Park et al June 23, 1959 2,905,804 Wakeley Sept. 22, 1959

